volcanoes. volcanoes and plate tectonics volcano is a mountain formed when layers of lava and...
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Volcanoes
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Volcanoes and Plate tectonics
Volcano is a mountain formed when layers of lava and volcanic ash erupt and build up
Most are dormant About 600 are active
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What cause Volcanoes
Magma is less dense then solid rock It slowly rises to the earths surface Flows out through an opening called a vent Lava cools quickly and forms igneous rock Opening at the top of the vent is called a crater Pyroclastic flow – massive avalanches of hot
glowing rock and gases (complete destruction)
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Where do Volcanoes Form 1. Divergent Boundaries
Mid Atlantic Ridge Forms long deep cracks called rifts where magma flows
from 2. Convergent boundaries
Cascade Mt. Range in Oregon and Washington Mt. Saint HelenPacific Ring of Fire
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3. Hot Spots Hawaiian Islands
Far from the edge of any plate
Some area of the mantle are hotter then others These hot spots melt rock which rise to the surface to
form volcanoes Once the volcano rises above the water it becomes an
island
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What determines how a volcano Erupts
Composition of the magma plays a big role in determining the manner in how a volcano erupts
Lave – more silica (silicon and oxygen) tend to be thicker and resists flow
Lava containing more iron and magnesium and less silica tend to flow easier
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Amount of water vapor in lava influences how lava erupts
More water (steam) the more pressure builds up and the more violent the eruption is
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Forms of Volcanoes
Three basic volcanoes Shield volcanoes Cinder volcanoes Composite volcanoes
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1. Shield
Quiet eruption Broad volcanoes Gently sloping sides Ex. Hawaiian , rift zones like Iceland
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Cinder Cone
Explosive Volcano Throws lava into the air, lava cools and hardens
Tephra – small- cinders , large – bombs Forms steep sides Sunset crater
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Composite Volcano
Can vary between quiet or violent Alternating layers of lava and tephra Convergent boundaries above subduction zone Mt. St. Helens
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Fissure Eruption Magma that is highly fluid can ooze from cracks or
fissures in earths surface
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